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this post was submitted on 03 Aug 2024
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How can a rocket and thrusters work in space when there is no atmosphere to push against? The space ship/rocket would stay still and all the thrust matter would just be ejected. - For example, If the rocket wants to turn left, it is always shown as firing a thruster from the right side that turns the rocket/ship to the left. But in a vacuum all that would happen is the matter that came out of the thruster would be sucked into the vacuum and spread out evenly. The ship would not move. 🤔 Nothing to push against.
Edit: I see now (from the more helpful replies) That it is not the rocket pushing back, but rather the combusting expanding fuel that is pushing the rocket forward. Which makes sense to me now.
Google says thrusters are similar, in that it is expanding steam etc.
I think you missed a /s
Given how many people think that railguns have no recoil because "there is no explosion" they might actually seriously believe what they just wrote.
Scientific illiteracy is through the roof.
Or maybe it's the same as it it's always been it's just that people that are scientifically illiterate are given platforms to speak their illiteracy as truth.
I remember when Falkon 9 was doing its first landings, the whole YouTube comments section was filled with flat earthers claiming it's a CGI. Now you can take a car and go watch landings in person, I wonder where all those people went.
Are you saying that I am scientifically illiterate? For asking a question about how a rocket that uses thrust could work in an environment with nothing to thrust against? I don't think it's a dumb question. Sure there may be an answer that I am yet to learn, but that is why I am asking the question and seeing what answers I get. Maybe you were born with all the knowledge of the human race, but the rest of us have to learn it. And some of it is true, and some of it is BS.
Am I saying you are scientifically illiterate?
Based on the previous statements, yes. However, as a matter of fact, not necessarily insult.
The good news is you're following up with questions and want to learn more, instead of doubling down. With curiosity you will become more literate.
The education system in the country you are from has failed you. Assuming you are in your mid-late teens, or older, scientific topics should have already been taught in what North America would call "middle school" (11-14 years old). That teaches you things like conservation of momentum.
There is a reason why it's called illiteracy, because there is an expectation that the baseline level of education everyone in developed countries receives teaches them the fundamentals of how the world around them works. Without this fundamental understanding it's not possible to understand more complex topics that build upon it, stunting growth.
I agree with you. Good comment. I am an interesting case, I was born in the west, and I'm back home now, but my parents traveled during my school years, and my education has holes. (One of which being how rockets work apparently! lol)
To answer your last comment, i think it must be the internet that makes the literate annoyed with the less literate, and the illiterate frustrated with the perceived arrogance of the literate. Back in time I would imagine that both parties would mix in separate circles and not share in conversations like this.
Thanks for your comments
You are scientifically illiterate if you are asking questions that have easily discoverable answers (as in this example, centuries of confirmed results)
The burn from the thrusters doesn't push against space, it pushes against the rocket.
For more easily discoverable answers to basic physics questions, perhaps take a physics 101 course. Or just Google your question.
Or do it the way you just did it... Cunningham's law and all that. But be aware that people will consider you scientifically illiterate if you do it the way you just did it.
Idk what you mean thrust against, but there's always equal and opposite forces. Say you were floating in space and were holding a hammer. You throw the hammer away from you. You will also move away from the hammer as it moves away from you (albeit at different speeds relative to each object's mass). The conservation of momentum.
https://youtu.be/Fp7D5D8Bqjc?si=KyIr0doj2Pinf6U5
Here's an Eli5 video on how rockets work.
https://youtu.be/jI-HeXhsUIg?si=UvtAkVdbPDYimitY
Chemical/liquid rockets and compressed gas thrusters are two different things with different functions. You’re right that lighting a fire in space won’t do much but make a cool firework. A thruster doesn’t so much push against space as it does nudge the ship in the other direction. Newton’s 3rd law and all that except the second “body” in this case isn’t something physical outside the ship but rather the force of the the gas leaving the thruster nozzle causing a recoil.
Aren't Railguns works of fiction?
https://youtu.be/O2QqOvFMG_A
Really thought these things were a work of fiction. I guess it's because in the movies they pretend it's a laser instead of a high velocity missile of some kind.
I think they missed grade school.
What do you mean by a /s?
/s is internet slang for tagging a comment as being sarcastic.
Since that is hard to convey over text.
Equal and opposite reaction.
There's a law for this. The matter is "pushing" against the ship, it doesn't have to push against anything else.
In fact having an atmosphere to push against actually reduces the effectiveness of thrust due to atmospheric pressure, which must be overcome. Which is why different engines are designed to run in atmosphere versus out of atmosphere.
If you throw a baseball in space you have transferred momentum to that baseball, pushing you back. You will move in the opposite direction (likely spin because you just imparted angular momentum onto yourself since you didn't throw from center of mass)
Yes this is the conservation of momentum.
https://youtu.be/Fp7D5D8Bqjc?si=KyIr0doj2Pinf6U5
A rocket does not work because there is "something to push against". Your initial assumption is flawed, so it's normal and expected that you cannot reason about this right now. A rocket works because there are gases that are ignited, looking to expand. This expanding force is applied to the nozzle, hence to the entire body of the rocket, and pushes it in the opposite direction : up
Imagine yourself floating in space with a heavy object held in your hands. Say an anvil. You push the anvil away. This gesture is going to push you back by some amount as well, since the anvil is so heavy. Well the rocket is you, and the burning fuel is the anvil. A rocket is just an object continually jettisoning weight behind it so it can move forward
The ignited fuel expands and pushes the rocket. Makes perfect sense to me now. Correct, my initial assumption is where the train of thought went off track! Thanks for the explanation!
Nice 👌🏼
A lot of people are offering explanations, but I think I'm going to give one too.
Think of recoil in a gun. If you don't have a mental image of it, watch a few youtube videos of people firing handguns. Look for videos of big, high-recoil handguns, like the Desert Eagle or the Magnum (or the Super Ruger Redhawk according to chat-GPT).
You need to get a good look at handguns pushed backwards as they are fired.
Now think about this: those bullets aren't pushing against an atmosphere. They are pushing only against the inside of a gun.
But when this tiny, tiny bullet pushes super-fast against the gun, using the gun to accelerate to incredibly high speeds very quickly... it pushes the gun really hard in the other direction.
Get that mental image into your head. Small object can push large object with a lot of force by kicking off of large object with insane speed.
Now: Take away the person holding the gun. Take away the planet. Take away the atmosphere. Put that gun in space and pull the trigger again. (Just make sure to use a gun that has modern ammunition that doesn't require oxygen to fire).
What happens to all that recoil? What does the recoil do to the gun now? The bullet still goes flying out of the chamber. Still does this by pushing against the gun.
Hopefully it should now be easy to imagine that the gun will start moving.
Rocket fuel is basically a tank full of bullets.
The main function of rocket fuel is "heavy stuff that is shoved out of the spaceship to make it move."
The reason we use highly explosive fuel is because "shoving heavy stuff away from you at the speed of a bullet" is going to move you more than "shoving heavy stuff away from you at normal speed."
Does this make any sense?
Helpful to picture it yeah thanks. I had assumed rockets "push" out the back. But I see now that it is the ignited fuel that pushes the rocket forward instead. Which would work in a vacuum. All makes sense to me now thanks 👍🏻
You're welcome. I'm glad I was able to help.
Every action has an equal and opposite reaction
Think of it like this, imagine you are in space and you throw a baseball in front of you, this action will cause an opposite reaction, moving you backwards
The same law which makes gun recoil happen. If you fire a pistol in vacuum you would still get the same recoil or even stronger. The rocket engine fires a lot of gas molecules instead of bullets at much higher velocity than a bullet, which gives it the constant push/recoil
You're on to something, I suppose, but the conservation of momentum does allow for travel in a vacuum. The matter ejected by the thruster pushes against the rocket.
They're not on to anything here. As further stated by your comment.
Yes I agree with you in that it would have the undisturbed momentum from pushing off from earth. But no way to slow down, or change course. I'm not sure mater ejected could push back. Surly the vacuum of space would just suck the rocket or thruster empty as fast as possible. . It just bugs me. Lol
It's very simple actually. If you want to change course or slow down you just eject mass in another direction. To slow down you just spin the rocket around and burn in the opposite direction (or you could have two engines in both directions if you wanted, but I don't think any rocket has that.)
Ejected in this case usually means very violently pushing fuel/gas in one direction. There isn't a small gnome sitting on the engine throwing blocks of fuel into space, even if they technically could have worked. Instead we use very powerful engines.
The ejection itself provides the push back, not the matter. Once the matter has been ejected it doesn't do jack shit.
I'm sure they close the valves when they aren't actively using the engine. It's not like fuel injectors in cars just constantly spray out fuel, even when parked.
It could be tested to a degree with a vacuum chamber here on earth. Put a little rocket inside horizontally and see if it moves when fired in a partial vacuum.
It might surprise you, but there have been numerous tests in vacuums on earth.
Also numerous tests in space.
Yup. You'd also have to discount satellites as fake if you choose to not believe in rockets. And also everything that satellites provide for us.
Plus, you know... basic physics.
Pff gps is a hoax, in reality there is a little goblin with a perfect sense of direction in your phone.
GPS: Goblin's Perfect Sense (but in the phone)